The present invention is directed to a display. More specifically, the present invention is directed to a display having photochromic characteristics. One embodiment of the present invention is directed to a display comprising an arrangement of a plurality of optically anisotropic rotatable elements, each of said rotatable elements having a surface in contact with an enabling fluid, said rotatable elements being electrically dipolar in the presence of the enabling fluid and thus being subject to rotation upon application of an electric field, said rotatable elements being free to rotate in place but not free to translate substantially so as to disrupt the arrangement of rotatable elements, wherein a first portion of said surface contains a mixture of a chelating agent and a spiropyran material of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, and wherein a second portion of said surface contains substantially no spiropyran.
Photochromism in general is a reversible change of a single chemical species between two states having distinguishably different absorption spectra, wherein the change is induced in at least one direction by the action of electromagnetic radiation. The inducing radiation, as well as the changes in the absorption spectra, are usually in the ultraviolet, visible, or infrared regions. In some instances, the change in one direction is thermally induced. The single chemical species can be a molecule or an ion, and the reversible change in states may be a conversion between two molecules or ions, or the dissociation of a single molecule or ion into two or more species, with the reverse change being a recombination of the two or more species thus formed into the original molecule or ion. Photochromic phenomena are observed in both organic compounds, such as anils, disulfoxides, hydrazones, oxazones, semicarbazones, stilbene derivatives, o-nitrobenzyl derivatives, spiro compounds, and the like, and in inorganic compounds, such as metal oxides, alkaline earth metal sulfides, titanates, mercury compounds, copper compounds, minerals, transition metal compounds such as carbonyls, and the like. Photochromic materials are known in applications such as photochromic glasses, which are useful as, for example, ophthalmic lenses.
Electric reusable paper can be defined as any electronically addressable display medium that approximates paper in form and function. Electric reusable paper ideally is light-weight, thin, and flexible, and ideally it displays images indefinitely while consuming little or no power. In addition, electric reusable ideally is reusable so that the user is able to erase images and create new ones repeatedly. Preferably, electric reusable paper displays images using reflected light and allows a very wide viewing angle.
One form of electric paper uses a gyricon or rotating element display. Gyricon or twisting ball displays typically are display systems in which the display panel comprises rotatable elements such as cylinders, prisms, or spherical balls that have an optical and an electrical anisotropy as a result of each hemisphere surface having a different color and a electrical charge in contact with a liquid. These rotatable elements are typically embedded in a solid substrate and a slight space between each rotatable element and the substrate is filled with a liquid so that the elements are free to rotate in a changing electrical field but cannot migrate from one location to another. If, for example, one hemisphere of the rotatable element is black and the other is white, each pixel can be turned on and off by the electrical field applied to that location. Each pixel can be individually addressed, and a full page image can thus be generated.
Most commonly the solid substrate used in these displays is a gel, typically a silicone gel. The purpose of using this material lies in the remarkably large expansion in volume exhibited by gels when soaked in certain liquids refered to as plasticizing liquids. Thirty percent expansions are not uncommon when these materials are soaked in silicone oils. The rotatable elements do not expand when contacted by the plasticizing liquid, so a cavity opens up around each rotatable element when the gel is immersed in a plasticizing liquid. This space fills with the plasticizing liquid.
Other variations on these displays are also known, such as embodiments wherein the rotatable elements are individually enclosed in shells with the space between the inner surface of the shell and the outer surface of the rotatable element being filled with a dielectric liquid. The resultant capsules can then be dispersed in a second liquid, such as an optically clear epoxy, which can then be hardened. The resultant display is then in the form of a thin, paper-like sheet. Alternatively, the resultant display can easily be conformally coated on a non-planar surface for even greater flexibility of applications.
Other variations on these displays include using rotatable elements of other than ball or sphere shape, such as cylinders, prisms, or the like.
In some embodiments, the display comprises a thin substantially transparent sheet having many of the attributes of paper documents. It looks like paper, has ambient light valve behavior like paper (i.e. the brighter the ambient light, the more easily it may be seen), is flexible like paper, can be folded like paper, can be carried around like paper, can be written on like paper, can be copied like paper, and has nearly the archival memory of paper since the display typically retains an image indefinitely in the absence of an applied electric field. These embodiments are frequently referred to as xe2x80x9celectric paperxe2x80x9d. The display provides a reuseable (and thus environmentally friendly) substitute for ordinary paper. In other embodiments, the display device has a rigid structure incorporating an array of addressing electrodes. Upon application of an electrical field between electrodes located on opposite surfaces of the layer containing the bichromal elements, the elements rotate depending on the polarity of the field, presenting one or the other hemisphere to an observer.
U.S. Pat. No. 5,633,109 (Jennings et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous liquid vehicle, a photochromic material, and a vesicle-forming lipid, wherein vesicles of the lipid are present in the ink.
U.S. Pat. No. 5,593,486 (Oliver et al.), the disclosure of which is totally incorporated herein by reference, discloses a hot melt ink composition comprising (a) an ink vehicle, said ink vehicle being a solid at about 25xc2x0 C. and having a viscosity of from about 1 to about 20 centipoise at a temperature suitable for hot melt ink jet printing, said temperature being greater than about 45xc2x0 C., (b) a photochromic material, (c) an optional colorant, and (d) an optional propellant.
U.S. Pat. No. 5,551,973 (Oliver et al.), the disclosure of which is totally incorporated herein by reference, discloses an ink composition which comprises an aqueous phase, an oil phase, a photochromic material, and a surfactant, said ink exhibiting a liquid crystalline gel phase at a first temperature and a liquid microemulsion phase at a second temperature higher than the first temperature.
U.S. Pat. No. 5,759,729 (Martin et al.), the disclosure of which is totally incorporated herein by reference, discloses a toner composition for the development of electrostatic latent images which comprises particles comprising a mixture of a resin and a photochromic material. Another embodiment of the present invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle and a photochromic material, wherein the liquid developer has a resistivity of from about 108 to about 1011 ohm-cm and a viscosity of from about 25 to about 500 centipoise. Yet another embodiment of the present invention is directed to a liquid developer composition for the development of electrostatic latent images which comprises a nonaqueous liquid vehicle, a charge control agent, and toner particles comprising a mixture of a resin and a photochromic material.
U.S. Pat. No. 5,710,420 (Martin et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of embedding and recovering machine readable information on a substrate which comprises (a) writing data in a predetermined machine readable code format on the substrate with a photochromic marking material having a first state corresponding to a first absorption spectrum and a second state corresponding to a second absorption spectrum; and (b) thereafter effecting a photochromic change in at least some of the photochromic marking material from the first state to the second state.
James T. C. Wojtyk, Peter M. Kazmaier, and Erwin Buncel, xe2x80x9cEffects of Metal Ion Complexation on the Spiropyran-Merocyanine Interconversion: Development of a Thermally Stable Photo-Switch,xe2x80x9d Chem. Commun. 1998, p. 1703, the disclosure of which is totally incorporated herein by reference, discloses spectrophotometric absorption and fluorescence measurements of spiropyrans 
modified with chelating functionalities, in the presence of Ca2+ and Zn2+, that provide evidence of a thermally stable spiropyran-merocyanine photoswitch that is modulated by the metal cations.
U.S. Pat. No. 4,126,854 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a display system in which the display panel comprises a plurality of particles which have an electrical anisotropy due to hemispherical surface coatings of different Zeta potential and their distribution in a volume of a dielectric liquid, and which also have an optical anisotropy due to the hemispherical surface coatings having different optical characteristics which may be due to the color or other optical properties of the hemispherical coatings. Under the action of an external electric field, the particles will rotate in accordance with their electrical anisotropy to provide a display in accordance with their optical anisotropy. The display has switching threshold and memory capabilities.
U.S. Pat. No. 4,143,103 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of making a display characterized by a plurality of particles which have an electrical anisotropy due to hemispherical surface coatings of different Zeta potential and their distribution in a volume of a dielectric liquid and which also have an optical anisotropy due to the hemispherical surface coatings having different optical characteristics. The particles are mixed with a light transparent liquid which is subsequently cured to form an elastomeric or rigid slab. Following curing of the liquid, the slab is emersed in a plasticizer (dielectric liquid) which is absorbed by the slab and which causes the slab to expand slightly. Expansion of the slab around the particles provides a plasticizer-filled cavity around each particle which cavities allow the particles to rotate to provide a display in accordance with their optical anisotropy but does not allow substantial translation of the particles.
U.S. Pat. No. 4,261,653 (Goodrich), the disclosure of which is totally incorporated herein by reference, discloses a light valve formed of a plurality of spherical dipolar particles suspended in a matrix material. Each spherical dipolar particle has a unified body formed in three discrete symmetrical sections. A central section is configured to permit light transmission when in a first orientation with respect to a path of light travel, and generally not permit light transmission when in a second, transverse orientation with respect to the path of light travel. A pair of intermediate sections bound the central section and are formed of a transparent material having an electrical permittivity that varies through a range of values as a function of the frequency of an applied electric field. A pair of outer sections bounds the intermediate sections and are formed of a material having a relatively stable electrical permittivity within the range of values of the intermediate sections. An applied electric field at one frequency extreme will cause the spherical dipolar particle to align in the first orientation to permit light transmission, and an applied electric field in the other frequency extreme will cause the particle to anti-align in the second, transverse orientation to shutter or reflect light. The matrix material is preferably formed of a plasticized elastomer that has a plurality of expanded cavities, with each cavity containing an outer lubricating layer to allow free rotational motion of a dipolar particle in the cavity. The use of a light valve of the present invention and method of manufacturing the spherical dipolar particle construction are also disclosed.
U.S. Pat. No. 4,438,160 (Ishikawa et al.), the disclosure of which is totally incorporated herein by reference, discloses a method for manufacturing rotary ball display devices wherein a plurality of such balls are provided with a coating of a color different from the remainder of the ball, the ball members are coated with a thin coating insoluble in the settling medium into which they are introduced, so that upon settling into a low viscosity liquid, they form a uniform layer. A high molecular weight hardenable coating material which is soluble in the low viscosity liquid is then poured onto the coated ball members to cover the layer. Then, the low viscosity liquid is removed and the hardenable coating material is caused to harden. The thin coating is then dissolved away from portions of the ball members to leave cavity portions thereabout into which a high resistivity liquid is introduced, The resulting ball members have a refractive index on the colored layer which is substantially the same as the refractive index of the high resistivity liquid contained in the cavities.
U.S. Pat. No. 5,389,945 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an addressable display system including a paper-like sheet comprising a light transparent host layer loaded with a plurality of repositionable elements, the elements are movable from a first orientation in which they will present a first visual appearance, to a second orientation in which they will present a second visual appearance, and independent external addressing means relatively movable with respect to the display sheet for affecting the orientation of the repositionabie elements.
U.S. Pat. No. 5,604,027 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses bichromal balls having two hemispheres, typically one black and one white, each having different electrical properties. Each ball is enclosed within a spherical shell and then a space between the ball and shell is filled with a liquid to form a microsphere so that the ball is free to rotate in response to an electrical field. The microspheres can then be mixed into a substrate which can be formed into sheets or can be applied to any kind of surface. The result is a film which can form an image from an applied electrical field.
U.S. Pat. No. 5,989,629 (Sacripante et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for the preparation of bichromal spheres comprising (i) preparing monochromal spheres by the aggregation and coalescence of an emulsion resin with a first colorant and inorganic salt; (ii) contacting the resulting monochromal spheres with an oxidizing agent, followed by a polymerization with a vinyl monomer and a free radical initiator; (iii) forming a monolayer of the resulting monochromal spheres on a substrate; and (iv) subjecting the resulting monochromal spheres to a vapor thermal deposition with a second colorant dissimilar than the first colorant thereby to coat one hemisphere of each of said monochromal spheres, thereby resulting in bichromal spheres with dissimilar colors.
U.S. Pat. No. 4,810,431 (Leidner), the disclosure of which is totally incorporated herein by reference, discloses a particle display comprising a plurality of particles which in an electrical field rotate to expose either their white or black surface depending upon the polarity of the field. The particle display can be used for a flat panel ambient-illuminated numeric, alpha-numeric and other forms of visual displays.
U.S. Pat. No. 5,262,098 (Crowley et al.), the disclosure of which is totally incorporated herein by reference, discloses an apparatus for fabricating hemispherically bichromal balls, comprising a separator member having opposing first and second surfaces located and an edge region in contact with both surfaces, and delivery means for flowing first and second colored hardenable liquid material over the first and second surfaces, respectively, so that the liquid materials arrive at the edge at substantially the same flow rate and form a reservoir outboard of the edge region. The reservoir comprises side-by-side regions of different colors which do not intermix. Further means is provided for propelling the first and second liquid materials away from the separator member and out of the reservoir into a fluid medium as a plurality of side-by-side bichromal streams whose forward ends become unstable and break up into droplets which form into spherical balls, each of the balls comprising hemispheres of differently colored hardenable liquid, and means for collecting the bichromal balls.
U.S. Pat. No. 5,344,594 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of forming hemispheric bichromal balls, including the steps of bringing together two streams of differently colored hardenable liquids for forming a single side-by-side bichromal stream, expelling said single side-by-side bichromal stream into a fluid as one or more free jets whose forward ends becomes unstable and break up into droplets which form into spherical balls, each of the balls comprising hemispheres of differently colored hardenable liquid, and finally hardening the balls.
U.S. Pat. No. 5,917,646 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a combination of an optically transmissive dielectric fluid having a first refractive index and an optically anisotropic particle rotatably disposed in the fluid. The particle has at least one optically transmissive region having a second refractive index. The particle provides a first optical modulation characteristic when disposed in the fluid in a first orientation with respect to a flux of optical energy, and further provides a second optical modulation characteristic when disposed in the fluid in a second orientation with respect to a flux of optical energy. The particle has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the particle electrically responsive such that when the particle is rotatably disposed in an electric field while the electrical dipole moment of the particle is provided, the particle tends to rotate to an orientation in which the electrical dipole moment aligns with the field. For example, the disposition of the particle in the fluid can give rise to the electrical dipole moment of the particle. The fluid-particle combination can be used to make a gyricon or rotating-particle display in which each rotatable particle (e.g., spherical ball) in the display acts as a lens.
U.S. Pat. No. 5,777,782 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or rotating-particle display having an auxiliary optical structure. The display includes a substrate with an optically transmissive window, a plurality of particles disposed in the substrate, and an optical focusing element optically coupled to the window. Each particle has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the particle electrically responsive such that when the particle is rotatably disposed in an electric field while the electrical dipole moment of the particle is provided, the particle tends to rotate to an orientation in which the electrical dipole moment aligns with the field. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate, when the particle is in this rotatable disposition, it is not attached to the substrate. Each particle, when rotatably disposed in the substrate, is disposable in first and second rotational orientations with respect to the optically transmissive window. Each particle provides a first optical modulation characteristic when disposed in its first orientation with respect to a flux of optical energy through the window, and further provides a second optical modulation characteristic when disposed in its second orientation with respect to a flux of optical energy through the window, The optical focusing element can be optically refractive; for example, it can include an array of converging lenses, such as a xe2x80x9cfly""s-eyexe2x80x9d array of microlenses. In this case, the particles can be disposed in an array that is registered with the lens array.
U.S. Pat. No. 5,815,306 (Sheridon et al.), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or rotating-particle display having an xe2x80x9ceggcratexe2x80x9d substrate. The display includes a substrate having a cavity-containing matrix whose cavities are disposed substantially in a single layer and are arranged within the matrix substantially in a geometrically regular pattern, and a plurality of optically anisotropic particles disposed in the cavities in the substrate, with each cavity containing at most one of the optically anistropic particles. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; the particle, when in its rotatable disposition, is not attached to the substrate. Each particle, for example, can have an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the particle electrically responsive such that when the particle is rotatably disposed in an electric field while the electrical dipole moment of the particle is provided, the particle tends to rotate to an orientation in which the electrical dipole moment aligns with the field. The single layer of cavities can be substantially planar, and the geometrical pattern of cavities can be a two-dimensional array pattern in the plane of the layer, such as a hexagonal, rectangular, or rhomboidal array pattern. The substrate can further include first and second members between which members the matrix is disposed; at least one of the members can include an optically transmissive window through which a flux of optical energy can pass so as to be incident on the particles.
U.S. Pat. No. 5,717,514 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a multisegmented ball for an electrical twisting ball display device made up of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. The segments include a first segment having a first thickness and a first optical modulation characteristic, a second segment having a second thickness and a second optical modulation characteristic, and a third segment having a thickness different from at least one of the first and second thicknesses and an optical modulation characteristic different from at least one of the first and second optical modulation characteristics. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. A method and apparatus for fabricating the ball are also disclosed.
U.S. Pat. No. 5,919,409 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of fabricating a multisegmented ball for an electrical twisting ball display device, which is made up of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. The method for fabricating the multisegmented spheroidal balls comprises the steps of first providing a multiplicity of liquid flows, each liquid flow having an associated flow rate, each liquid flow being a flow of a hardenable liquid material associated with an optical modulation characteristic. The multiplicity of flows are then merged into a combined liquid flow where each one of the plurality of liquid flows is joined to at least one other of the plurality of liquid flows at a planar interface. After forming a combined liquid flow, a ligament is formed from the combined liquid flow and a plurality of spheroidal balls are formed from the ligament, each of the balls comprising a multiplicity of segments where each one of the multiplicity of segments is joined to at least one other of the multiplicity of segments at a planar interface. After the balls are formed they are hardened.
U.S. Pat. No. 5,891,479 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an apparatus for fabricating a multisegmented ball for an electrical twisting ball display device, which is made up of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. The apparatus has a plurality of separator members, each separator member having two opposed surfaces and an edge region in contact with both of said surfaces. A liquid flow is associated with each separator member and one of the surfaces on the separator member. Each one of the liquid flows is provided across its associated separator members toward the edge region of the separator member. Each of the liquid flows is of a hardenable liquid material and has an optical modulation characteristic and a flow rate. The apparatus also has apparatus for merging the liquid flows outboard of the edge regions of the separator members into a combined liquid flow and then apparatus for forming a ligament from the combined liquid flow. Apparatus for forming a plurality of spheroidal balls from the ligament; and apparatus for hardening the balls thus formed complete the apparatus.
U.S. Pat. No. 5,708,525 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a multisegmented ball for an electrical twisting ball display device made up of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another. Each segment is adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. Each segment has an optical modulation characteristic, the optical modulation characteristics of adjacent segments being different from one another. The segments of the ball include a first exterior segment, a second exterior segment, and a transparent interior segment. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field, Also disclosed are: a material made up of a substrate in which are disposed the aforementioned balls; an apparatus made up of a piece of this material, together with electrodes to facilitate a rotation of balls rotatably disposed therein; and a method for using this apparatus.
U.S. Pat. No. 5,717,515 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method for producing a canted electric field for an electrical twisting ball display device made up of electrically and optically anisotropic spheroidal balls rotatably disposed in a substrate. The display has an array of addressable elements, each array element including at least one spheroidal ball. According to the method, an array element is selected. A preferred direction of orientation is selected for balls of the selected array element, the direction of orientation forming an angle with a vector normal to a planar portion of the substrate surface in a vicinity of the selected array element, the angle being greater than 0 degree and less than 180 degrees. Balls of the selected array element are aligned with the preferred direction of orientation by applying an electric field in the vicinity of the selected array element, the electric field having an electric field vector oriented parallel to the selected preferred direction, thereby causing balls of the selected array element to rotate so as to align with the preferred direction of orientation, Also disclosed are: an electrode assembly for addressing a twisting ball display, capable of producing an electric field adjustable as to the direction of orientation of the field over a continuous angular range of directions, and a twisting ball apparatus incorporating this electrode assembly.
U.S. Pat. No. 5,760,761 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a multisegmented, highlight color ball for an electrical twisting ball display device made up of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. Each segment has an optical modulation characteristic, the optical modulation characteristics of adjacent segments being different from one another. The segments include: a central segment having a thickness; a first interior segment, situated adjacent to the central segment and having a thickness less than the central segment thickness; a second interior segment, situated opposite the first interior segment with respect to the central segment and having a thickness less than the central segment thickness; a first exterior segment; and a second exterior segment. The central segment can be of a background color; the first interior segment can be of a foreground color; the second interior segment can be of a highlight color; and the exterior segments can be transparent. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Also disclosed are: an apparatus made up of a substrate in which are disposed the aforementioned balls, together with electrodes to facilitate a rotation of balls rotatably disposed therein; and a method for using this apparatus.
U.S. Pat. No. 5,751,268 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a seven-segment ball for an electrical twisting ball display device made up of spheroidal balls rotatably disposed in an elastomer substrate. The device built with the seven-segment balls can provide, for example, two fully saturated colors, two partially saturated colors, and a background color, such as white. The ball is composed of seven segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments, adjacent segments being adjoined to one another at substantially planar interfaces. The seven segments include a transparent central segment, transparent first and second exterior segments, and four colored interior segments, two on each side of the central segment. For example, the first, second, third, and fourth interior segments can each have different colors such as red, black, blue, and green. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Also disclosed are: an apparatus made up of a substrate in which are disposed the aforementioned balls, together with electrodes to facilitate a rotation of balls rotatably disposed therein; and a method for using this apparatus.
U.S. Pat. No. 5,892,497 (Robertson), the disclosure of which is totally incorporated herein by reference, discloses a segmented ball for an electrical twisting ball color display device, the device being composed of different sets of spheroidal balls rotatably disposed in an elastomer substrate, each set being associated with a different display color. The segmented ball includes a colored interior segment surrounded on either side by transparent exterior segments, the three segments being arrayed substantially parallel to one another, with adjacent segments being adjoined to one another at substantially planar interfaces. The colored interior segment can have, for example, a transparent or opaque chromatic color, such as red, green, or blue. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Also disclosed are: a material made up of a substrate in which are disposed two or more different sets of the aforementioned balls, each set having a different center-segment color so as to provide a different observable display color; an apparatus made up of a piece of this material, together with electrodes to facilitate a rotation of balls rotatably disposed therein; and a method for using this apparatus.
U.S. Pat. No. 5,767,826 (Sheridon et al.), the disclosure of which is totally incorporated herein by reference, discloses a multilayer substrate material for a subtractive-color electrical twisting ball display. The material is composed of a layered substrate including first, second, and third layers, each layer of the substrate being a nearest neighboring layer with respect to at least one other layer and no more than two other layers. Spheroidal balls are disposed in each of the first, second, and third layers. In the first layer, each ball has at least two component regions including a component region having a first chromatic color, such as transparent cyan. In the second layer, each ball has at least two component regions including a component region having a second chromatic color, such as transparent magenta. In the third layer, each ball has at least two component regions including a component region having a third chromatic color, such as transparent yellow. Optionally, the substrate can further include a fourth layer in which are disposed spheroidal balls, each having at least two component regions including a black component region. Each ball in each layer has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Also disclosed are a twisting-ball apparatus made with the material, and a method for using this apparatus.
U.S. Pat. No. 5,739,801 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a multithreshold electrical twisting ball display device. The device is composed of electrically and optically anisotropic spheroidal balls of at least two different rotation thresholds, disposed in an elastomer substrate, together with an addressing electrode assembly. The addressing electrode assembly allows a preferred region of the substrate to be selected in which at least one ball of the first set and at least one ball of the second set are disposed, and first and second electric fields to be applied to the preferred region thus selected, each of the first and second electric fields extending throughout the preferred region. The first field facilitates a contemporaneous rotation of balls of both the first and second sets rotatably disposed in the preferred region. The second electric field facilitates a rotation of balls of the second set rotatably disposed in the preferred region, without facilitating a rotation of any ball of the first set rotatably disposed in the preferred region. Also disclosed are the substrate material and electrode assembly for the device, and a method of using the device.
U.S. Pat. No. 5,982,346 (Sheridon et al.), the disclosure of which is totally incorporated herein by reference, discloses a method of making a substrate in which sets of optically anisotropic spheroidal balls are disposed, as for use in an electrical twisting ball display. First and second sets of spheroidal balls, are deposited on a receiving surface composed of an elastomer substrate material in an adhesive state, the spheroidal balls thus deposited adhering to the receiving surface. Balls of the first and second sets are physically distinguishable from one another. Balls of the first set can be deposited in a first arrangement, and balls of the second set, in a second arrangement. Each ball of each set has an optical anisotropy and an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in an electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. With the balls thus deposited, additional, liquid elastomer material is poured over the balls adhering to the receiving surface, thereby covering the balls and forming an uncured substrate material in which the balls are disposed. This uncured substrate material is cured to form a substrate in which balls of the first and second sets are disposed. A plasticizer fluid can be applied to the substrate thus formed, thereby expanding the substrate so as to render the balls disposed in the substrate rotatable within the substrate.
U.S. Pat. No. 5,737,115 (Mackinlay et al.), the disclosure of which is totally incorporated herein by reference, discloses a tristate light valve ball for an electrical twisting ball device composed of spheroidal balls rotatably disposed in an elastomer substrate. The ball is composed of segments arrayed substantially parallel to one another, each segment being adjacent to at least one other segment and to no more than two other segments. Adjacent segments are adjoined to one another at substantially planar interfaces. The segments include: a first, interior, nontransparent segment having a first optical modulation characteristic; a second exterior, transparent segment, adjacent to the first segment and having a second optical modulation characteristic; a third, interior, nontransparent segment having a third optical modulation characteristic; and a fourth, exterior, transparent segment adjacent to the third segment. For example, the ball can be made with a black first segment adjacent to a white third segment, surrounded on either side by clear second and fourth exterior segments. The ball has an anisotropy for providing an electrical dipole moment, the electrical dipole moment rendering the ball electrically responsive such that when the ball is rotatably disposed in a nonoscillating electric field while the electrical dipole moment of the ball is provided, the ball tends to rotate to an orientation in which the electrical dipole moment aligns with the field. Also disclosed are: a material made up of a substrate layer in which are disposed the aforementioned balls, with a colored backing joined to a rear surface of the layer; and a method for using a device incorporating the balls.
U.S. Pat. No. 5,754,332 (Crowley), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or twisting-ball display having superior reflectance characteristics comparing favorably with those of white paper. The display is based on a material made up of optically anisotropic particles, such as bichromal balls, disposed substantially in a monolayer in a substrate. The particles are closely packed with respect to one another in the monolayer, preferably so that adjacent particle surfaces are as close to one another as possible. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; for example, the particles can already be rotatable in the substrate, or can be rendered rotatable in the substrate by a nondestructive operation performed on the substrate. In particular, the particles can be situated in an elastomer substrate that is expanded by application of a fluid thereto so as to render the particles rotatable therein. A particle, when in its rotatable disposition, is not attached to the substrate. A reflective-mode display apparatus can be constructed from a piece of the material together a mechanism (e.g., addressing electrodes) for facilitating rotation of at least one of the particles. The light reflected from the display is reflected substantially entirely from the monolayer of balls, so that lower layers are not needed. By eliminating the lower layers, the display can be made thinner, which in turn provides further advantages, such as lower drive voltage and better resolution due to better control of fringing fields.
U.S. Pat. No. 5,808,783 (Crowley), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or twisting-ball display having superior reflectance characteristics comparing favorably with those of white paper. The display is based on a material made up of optically anisotropic particles, such as bichromal balls, disposed in a substrate having a surface. The particles situated closest to the substrate surface form substantially a single layer. Each particle in the layer has a center point, no particle in the layer being disposed entirely behind the center point of any nearest neighboring particle in the layer with respect to the substrate surface. Each particle in the layer has a projected area with respect to the substrate surface. Particles of the set are sufficiently closely packed with respect to one another in the layer that the union of their projected areas exceeds two-thirds of the area of the substrate surface. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; for example, the particles can already be rotatable in the substrate, or can be rendered rotatable in the substrate by a nondestructive operation. In particular, the particles can be situated in an elastomer substrate that is expanded by application of a fluid thereto so as to render the particles rotatable therein. A particle, when in its rotatable disposition, is not attached to the substrate. A reflective-mode display apparatus can be constructed from a piece of the material together with a mechanism (e.g., addressing electrodes) for facilitating rotation of at least one of the particles.
U.S. Pat. No. 5,914,805 (Crowley), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or twisting-ball display having superior reflectance characteristics comparing favorably with those of white paper is based on a material made up of two populations (e.g., two different sizes) of optically anisotropic particles, such as bichromal balls, disposed in a substrate. Particles of the first population, as considered by themselves without the particles of the second population, are disposed in the substrate in a closely packed (e.g., geometrically regular) arrangement having interstices. Particles of the second population are disposed in the interstices of the arrangement. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; for example, the particles can already be rotatable in the substrate, or can be rendered rotatable in the substrate by a nondestructive operation performed on the substrate. In particular, the particles can be situated in an elastomer substrate that is expanded by application of a fluid thereto so as to render the particles rotatable therein. A particle, when in its rotatable disposition, is not attached to the substrate. A reflective-mode display apparatus can be constructed from a piece of the material together with a mechanism (e.g., addressing electrodes) for facilitating rotation of at least one of the particles.
U.S. Pat. No. 5,825,529 (Crowley), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or twisting-ball display in which optically anisotropic particles, such as bichromal balls, are disposed directly in a working fluid, such as a dielectric liquid, without an elastomer substrate or other cavity-containing matrix. The display apparatus has an optically transmissive viewing surface, behind which the working fluid is disposed with the particles in it. The particles are arranged in a closely packed stable arrangement in which neighboring particles tend to keep one another in place. For example, the particles can be arranged in a hexagonally packed monolayer. The working fluid does not substantially constrain the particles to remain in the stable arrangement, notwithstanding the direct contact of the fluid with the particles.
U.S. Pat. No. 6,147,791 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a sheet material for use in a gyricon display in which a rotatable element, which has a portion which is capable of being permanently magnetized may be oriented to experience an attractive force between itself and a soft magnetic material pad. The attractive force between the element and the pad serve to latch the element in place and prevent unwanted display changes from taking place. The element may be constructed to be either cylindrically or spherically shaped. The element and the soft magnetic material pads may be arranged to provide multiple latching states as desired.
U.S. Pat. No. 6,097,531 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of forming magnetized rotating elements for a rotating element display where all the elements are magnetized in the same orientation is provided. First, at least two planar streams of hardenable liquids flowing in substantially the same direction are provided. Each stream has an associated optical modulation characteristic and at least one stream has an associated optical modulation characteristic different from at least one other stream. At least one stream includes a magnetic pigment. The streams are then merged to form a reservoir containing side-by-side amounts of each liquid from each stream. A free jet is then formed containing side-by-side amounts of each liquid from the reservoir, Then a portion of the free jet is passed through a magnetic field which is oriented transverse to the direction of the free jet to magnetize the magnetic pigment. The rotating elements formed can be either spherical in shape or cylindrical in shape. In either case, each element will comprise side-by-side segments. To form spherical elements the free jet can be broken into spherical portions either before or after the magnetic pigment has been magnetized. Ultimately, magnetized spherical portions of the free jet are hardened into rotating spherical elements and collected. To form cylindrical elements, the free jet is magnetized and hardened into a filament. The filament is then collected and broken into cylindrical elements.
U.S. Pat. No. 6,174,153 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an apparatus for forming magnetized rotating elements for a rotating element display where all the elements are magnetized in the same orientation is disclosed. The apparatus comprises at least one separator member. Each separator member has a diameter, two opposed surfaces and an edge region in contact with both of the surfaces. Further included is an apparatus for providing at least two liquid flows wherein each one of the liquid flows has an associated separator member and an associated surface on the associated separator member, and each one of the liquid flows is provided across the associated surface of the associated separator members. The liquid flow flows toward the edge region of the associated separator member. The liquid flows are each a flow of hardenable liquid material associated with an optical modulation characteristic, and at least one of the liquid flows containing a magnetic pigment. The separator members are spun and the liquid flows are merged outboard of the edge regions of the one separator members to form a reservoir containing side-by-side amounts of each liquid. When the flow rate of the liquids is high enough, a free jet approximately in a plane outward from the reservoir, the free jet comprising side-by-side amounts of each liquid from the reservoir is formed. A magnetic field, is provided outward from the formation of the free jet and at least a portion of the free jet is passed through the magnetic field to magnetize the magnetic pigment. The magnetic field is aligned transverse to the free jet. If cylindrical elements are desired then the magnetized free jet is hardened into filaments which can be separated into cylindrical elements. If spherical elements are desired then the free jet is broken up into spherical elements before hardening.
U.S. Pat. No. 6,110,538 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of making rotating element sheet material utilizing magnetic latching. The first step is providing a sheet of sheet material comprising a substrate with a surface and rotatable elements disposed therein. The elements each have an optical and electrical anisotropy, and comprise at least two portions. One of the portions is magnetizable. After the magnetizable portions have been oriented in a common direction, they are magnetized substantially uniformly. The elements can be oriented such that the magnetized portions are disposed towards the surface of the substrate. A layer of hardenable mixture containing a plurality of magnetic particles is then applied to the surface of the substrate. The hardenable liquid is kept liquid for a period of time to allow the migration magnetic particles to the area of the layer in the vicinity of the magnetized portions of the rotatable elements. Then the hardenable liquid is solidified to trap the magnetic particles in said layer in the area of the layer in the vicinity of the magnetized portion of the rotatable elements to form a magnetic pad.
U.S. Pat. No. 6,038,059 (Silverman), the disclosure of which is totally incorporated herein by reference, discloses several variations in full-color additive gyricons are shown. Each gyricon shown has been designed for ease of construction by eliminating the need for precise placement of rotating elements, alignment between the gyricon layers, if any, and alignment between the gyricon sheet and the addressing device.
U.S. Pat. No. 6,122,094 (Silverman), the disclosure of which is totally incorporated herein by reference, discloses several variations in full-color additive gyricons. Each gyricon shown has been designed for ease of construction by eliminating the need for precise placement of rotating elements, alignment between the gyricon layers, if any, and alignment between the gyricon sheet and the addressing device.
U.S. Pat. No. 6,162,321 (Silverman), the disclosure of which is totally incorporated herein by reference, discloses several variations in full-color additive gyricons. Each gyricon shown has been designed for ease of construction by eliminating the need for precise placement of rotating elements, alignment between the gyricon layers, if any, and alignment between the gyricon sheet and the addressing device.
U.S. Pat. No. 6,128,124 (Silverman), the disclosure of which is totally incorporated herein by reference, discloses several variations in full-color additive gyricons. Each gyricon shown has been designed for ease of construction by eliminating the need for precise placement of rotating elements, alignment between the gyricon layers, if any, and alignment between the gyricon sheet and the addressing device.
U.S. Pat. No. 6,197,228 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses a method of making rotating element sheet material utilizing magnetic latching. First a plurality of rotating elements, each element having a magnetized segment, are mixed with an elastomer and a plurality of magnetic particles to attract the magnetic particles to the magnetized segments. Then a magnetic field is applied to orient the elements in a common direction. When the rotating elements have all been oriented in a common direction, they are held in that orientation for a long enough period of time to allow the magnetic particles to migrate in the elastomer to the regions of the elastomer in the vicinity of the magnetized segments of the elements. The elastomer is then cured to form an elastomer substrate with trapped rotating elements and magnetic particles. The elastomer substrate is then immersed into a bath of dielectric plasticizer which is absorbed more readily by elastomer than by the rotating elements. The elastomer substrate swells to create plasticizer-filled voids around the rotating elements. The magnetic particles remain incorporated within the elastomer to form magnetic material pads which are associated with an element.
U.S. Pat. No. 6,055,091 (Sheridon et al.), the disclosure of which is totally incorporated herein by reference, discloses a gyricon or twisting-particle display based on nonspheroidal (e.g., substantially cylindrical) optically anisotropic particles disposed in a substrate. The particles can be bichromal cylinders, preferably aligned parallel to one another and packed close together in a monolayer. A rotatable disposition of each particle is achievable while the particle is thus disposed in the substrate; for example, the particles can already be rotatable in the substrate, or can be rendered rotatable in the substrate by a nondestructive operation performed on the substrate. In particular, the substrate can be made up of an elastomer that is expanded by application of a fluid thereto so as to render the particles rotatable therein. A particle, when in its rotatable disposition, is not attached to the substrate. The close-packed monolayer configuration of particles provides excellent brightness characteristics and relative ease of manufacture as compared with certain other high-brightness gyricon displays. The substrate containing the cylinders can be fabricated with the swelled-elastomer techniques known from spherical-particle gyricon displays, with a simple agitation process step being used to align the cylinders within the sheeting material. Techniques for fabricating the cylinders are also disclosed.
U.S. Pat. No. 5,894,367 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an electric type paper display having memory properties, rapid response times, and multi-optical optical property display with an image of high quality. Each display element is wholly in contact with liquid in a cavity and the surface of each display element has a portion with a most positive charge. When an electrical field is applied from the outside, each display element is turned correspondingly to the direction of the electric field and, then electrically migrated through the liquid and attached to the inner surface of the cavity. Among multiple display surfaces of each display element an optical property is selected according to an image signal and is visible through a transparent support to an observer. Afterwards, the attached state of each display element, i.e., its display state is held by the action of an attraction force such as van der Waals force and electrostatic force acting between the circumferential surface of the display element and the inner surface of the cavity, even after the electric field is removed.
U.S. Pat. No. 5,922,268 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an electric type paper display having memory properties, rapid response times and multi-optical property display with an image of high quality. Each display element is wholly in contact with liquid in a cavity and the surface of each display element has a portion with a most positive charge. When an electrical field is applied from the outside, each display element is turned correspondingly to the direction of the electric field and, then electrically migrated through the liquid and attached to the inner surface of the cavity. Among multiple display surfaces of each display element an optical property is selected according to an image signal and is visible through a transparent support to an observer. Afterwards, the attached state of each display element, i.e., its display state is held by the action of an attraction force such as van der Waals force and electrostatic force acting between the circumferential surface of the display element and the inner surface of the cavity, even after the electric field is removed.
U.S. Pat. No. 5,904,790 (Sheridon), the disclosure of which is totally incorporated herein by reference, discloses an electric type paper display having memory properties, rapid response times and multi-optical property display with an image of high quality is made. Each display element is wholly in contact with liquid in a cavity and the surface of each display element has a portion with a most positive charge. When an electrical field is applied from the outside, each display element is turned correspondingly to the direction of the electric field and, then electrically migrated through the liquid and attached to the inner surface of the cavity. Among multiple display surfaces of each display element an optical property is selected according to an image signal and is visible through a transparent support to an observer. Afterwards, the attached state of each display element, i.e., its display state is held by the action of an attraction force such as van der Waals force and electrostatic force acting between the circumferential surface of the display element and the inner surface of the cavity, even after the electric field is removed.
Sheridon, xe2x80x9cThe Gyriconxe2x80x94A Twist Ball Display,xe2x80x9d Proceedings of the Society of Information Display, Vol, 18/3 and 4 (1977), the disclosure of which is totally incorporated herein by reference, discloses a gyricon ambient light viewed display consisting of an elastomer sheet contained between transparent electrodes. The elastomer sheet changes from black to white or from white to black depending upon the polarity of the electrical field that is impressed between the electrodes. The elastomer sheet contains a high loading of small balls that are black on one hemisphere and white on the other. Each ball is contained in an individual oil-filled spherical cavity and is free to rotate in response to the applied electric field.
U.S. Pat. No. 3,612,758 (Evans et al.), the disclosure of which is totally incorporated herein by reference, discloses a color display device employing the electrophoretic migration of color pigment particles to form an image on a matrix addressable panel. One coordinate terminal is connected to a line reservoir containing electrophoretic ink particles of a given polarity while the other coordinate terminal is connected to a transparent conductor. The panel is viewed through the transparent conductor side in ambient illumination.
U.S. Pat. No. 5,930,026 (Jacobson et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic display which has a substantially two-dimensional arrangement of microcapsules each having therein an electrophoretic composition of a dielectric fluid and a suspension of particles that visually contrast with the dielectric liquid and also exhibit surface charges; a pair of electrodes, at least one of which is visually transparent, disposed on and covering opposite sides of the microcapsule arrangement; and means for creating a potential difference between the two electrodes, the potential difference causing the particles to migrate toward one of the electrodes. The display may be powered by one or more piezoelectric elements, which are also suitable for powering other types of nonemissive displays.
U.S. Pat. No. 5,961,804 (Jacobson et al.), the disclosure of which is totally incorporated herein by reference, discloses an application-ready electrophoresis material includes a carrier and a dispersion of microcapsules therein, the microcapsules each containing a plurality of phases therein. At least some of the phases contrast visually and and exhibit differential responsiveness to an electric field, such that application of the field determines the visual appearance of the microcapsules. The material exhibits stability such the visual appearance persists despite removal of the field. In one aspect, the invention provides for enhanced stability of the visual appearance. In another aspect, the reflectivity of at least one of the phases is enhanced. In another aspect, one of the phases is particulate in nature and emits visible radiation.
U.S. Pat. No. 6,017,584 (Albert et al.), the disclosure of which is totally incorporated herein by reference, discloses electrophoretic displays and materials useful in fabricating such displays. In particular, encapsulated displays are disclosed. Particles encapsulated therein are dispersed within a suspending, or electrophoretic, fluid. This fluid may be a mixture of two or more fluids or may be a single fluid. The displays may further comprise particles dispersed in a suspending fluid, wherein the particles contain a liquid. In either case, the suspending fluid may have a density or refractive index substantially matched to that of the particles dispersed therein. Also disclosed are electro-osmotic displays. These displays comprise at least one capsule containing either a cellulosic or gel-like internal phase and a liquid phase, or containing two or more immiscible fluids. Application of electric fields to any of the electrophoretic displays described affects an optical property of the display.
U.S. Pat. No. 6,067,185 (Albert et al.), the disclosure of which is totally incorporated herein by reference, discloses electrophoretic displays and materials useful in fabricating such displays. In particular, encapsulated displays are disclosed. Particles encapsulated therein are dispersed within a suspending, or electrophoretic, fluid. This fluid may be a mixture of two or more fluids or may be a single fluid. The displays may further comprise particles dispersed in a suspending fluid, wherein the particles contain a liquid. In either case, the suspending fluid may have a density or refractive index substantially matched to that of the particles dispersed therein. Finally, also disclosed are electro-osmotic displays. These displays comprise at least one capsule containing either a cellulosic or gel-like internal phase and a liquid phase, or containing two or more immiscible fluids. Application of electric fields to any of the electrophoretic displays affects an optical property of the display.
U.S. Pat. No. 6,118,426 (Albert et al.), the disclosure of which is totally incorporated herein by reference, discloses a process for creating an electronically addressable display including multiple printing operations, similar to a multi-color process in conventional screen printing. In some of the process steps, electrically non-active inks are printed onto areas of the receiving substrate, and in other steps, electrically active inks are printed onto different areas of the substrate. The printed display can be used in a variety of applications. This display can be used as an indicator by changing state of the display after a certain time has elapsed, or when a certain pressure, thermal, radiative, moisture, acoustic, inclination, pH, or other threshold is passed. In one embodiment, the display is incorporated into a battery indicator. A sticker display is described. The sticker is adhesive backed and may then be applied to a surface to create a functional information display unit. This invention also features a display that is both powered and controlled using radio frequencies. It describes a complete system for controlling, addressing, and powering a display. The system includes an antenna or antennae, passive charging circuitry, and active control system, a display, and an energy storage unit. There is also a separate transmitter that provides the remote power for the display. The system is meant to be used anywhere it is useful to provide intermittent updates of information such as in a store, on a highway, or in an airport. A tile-based display allowing a modular system for large area display is created using a printable display material.
U.S. Pat. No. 6,120,588 (Jacobson), the disclosure of which is totally incorporated herein by reference, discloses a system of electronically active inks which may include electronically addressable contrast media, conductors, insulators, resistors, semiconductive materials, magnetic materials, spin materials, piezoelectric materials, optoelectronic, thermoelectric or radio frequency materials. Also disclosed is a printing system capable of laying down said materials in a definite pattern. Such a system may be used for instance to: print a flat panel display complete with onboard drive logic; print a working logic circuit onto any of a large class of substrates; print an electrostatic or piezoelectric motor with onboard logic and feedback or print a working radio transmitter or receiver.
U.S. Pat. No. 6,120,839 (Comiskey et al.), the disclosure of which is totally incorporated herein by reference, discloses electrophoretic displays and materials useful in fabricating such displays. In particular, encapsulated displays are disclosed. Particles encapsulated therein are dispersed within a suspending, or electrophoretic, fluid. This fluid may be a mixture of two or more fluids or may be a single fluid. The displays may further comprise particles dispersed in a suspending fluid, wherein the particles contain a liquid. In either case, the suspending fluid may have a density or refractive index substantially matched to that of the particles dispersed therein. Also disclosed are electro-osmotic displays. These displays comprise at least one capsule containing either a cellulosic or gel-like internal phase and a liquid phase, or containing two or more immiscible fluids. Application of electric fields to any of the electrophoretic displays described affects an optical property of the display.
U.S. Pat. No. 6,124,851 (Jacobson), the disclosure of which is totally incorporated herein by reference, discloses an electronic book comprising multiple, electronically addressable, page displays. Said page displays may be formed on flexible, thin substrates. Said book may additionally encompass memory, power, control functions and communications.
U.S. Pat. No. 6,130,773 (Jacobson et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic display having a substantially two-dimensional arrangement of microcapsules each having therein an electrophoretic composition of a dielectric fluid and a suspension of particles that visually contrast with the dielectric liquid and also exhibit surface charges; a pair of electrodes, at least one of which is visually transparent, disposed on and covering opposite sides of the microcapsule arrangement; and a power source for creating a potential difference between the two electrodes, the potential difference causing the particles to migrate toward one of the electrodes. The display may be powered by one or more piezoelectric elements, which are also suitable for powering other types of nonemissive displays.
U.S. Pat. No. 6,130,774 (Albert et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic display element including a capsule having a first, larger surface and a second, smaller surface. The capsule contains a suspending fluid and at least one particle dispersed within said suspending fluid. Application of a first electrical field causes the particle or particles to migrate towards the first, larger surface of the capsule, causing it to take on the visual appearance of the particles. Application of a second electrical field causes the particle or particles to migrate towards the second, smaller surface, allowing the capsule to take on the visual appearance of the dispersing fluid or of a substrate or electrode positioned behind the display element. Displays may be fabricated from multiple display elements arranged on a substrate.
U.S. Pat. No. 6,172,798 (Albert et al.), the disclosure of which is totally incorporated herein by reference, discloses an electrophoretic display element which includes a capsule having a first, larger surface and a second, smaller surface. The capsule contains a suspending fluid and at least one particle dispersed within said suspending fluid. Application of a first electrical field causes the particle or particles to migrate towards the first, larger surface of the capsule, causing it to take on the visual appearance of the particles. Application of a second electrical field causes the particle or particles to migrate towards the second, smaller surface, allowing the capsule to take on the visual appearance of the dispersing fluid or of a substrate or electrode positioned behind the display element. Displays may be fabricated from multiple display elements arranged on a substrate.
U.S. Pat. No. 6,177,921 (Comiskey et al.), the disclosure of which is totally incorporated herein by reference, discloses addressing schemes for controlling electronically addressable displays including a scheme for rear-addressing displays, which allows for in-plane switching of the display material. Other schemes include a rear-addressing scheme which uses a retroreflecting surface to enable greater viewing angle and contrast. Another scheme includes an electrode structure that facilitates manufacture and control of a color display. Another electrode structure facilitates addressing a display using an electrostatic stylus. Methods of using the disclosed electrode structures are also disclosed. Another scheme includes devices combining display materials with silicon transistor addressing structures.
While known compositions and processes are suitable for their intended purposes, a need remains for improved display apparatus. In addition, a need remains for display apparatus capable of exhibiting two or more colors. Further, a need remains for display apparatus having photochromic characteristics. Additionally, a need remains for display apparatus with photochromic characteristics wherein the photochromic material is thermally stable. There is also a need for display apparatus with photochromic characteristics wherein both resonance forms of the photochromic material are stable. In addition, there is a need for display apparatus with photochromic characteristics wherein the two resonance forms of the photochromic material are addressable at different wavelengths. Further, there is a need for display apparatus with photochromic characteristics wherein both resonance forms of the photochromic material are stable for reasonable periods of time without the need for constant irradiation to maintain the resonance form.
The present invention is directed to a display comprising an arrangement of a plurality of optically anisotropic rotatable elements, each of said rotatable elements having a surface in contact with an enabling fluid, said rotatable elements being electrically dipolar in the presence of the enabling fluid and thus being subject to rotation upon application of an electric field, said rotatable elements being free to rotate in place but not free to translate substantially so as to disrupt the arrangement of rotatable elements, wherein a first portion of said surface contains a mixture of a chelating agent and a spiropyran material of the formula 
wherein n is an integer representing the number of repeat xe2x80x94CH2xe2x80x94 units and R is xe2x80x94H or xe2x80x94CHxe2x95x90CH2, and wherein a second portion of said surface contains substantially no spiropyran.